Standard screws and barrels are manufactured out of high-alloyed steel, which is extra depth nitrated by GTS explicitly by gas nitriding. Combined with GTS design these screws are for most application the most economical version and show a very long operating time.
For special application GTS offers screws with armored flights, manufactured in PTA process. This often is made in combination with a special chrome coating within the flights. Usually PTA welded screws are used with a bimetallic barrel.
If the requirement specification or wear potential of formula is higher, completely coated screws and barrels are used. Jacketing material is a special alloy of Tungsten Carbide, which guarantees a very high wear protection on the running surface as well as in the screw flights. The twin screw barrels are coated with the same formula at the inner running surface. This combination of hardest wear protection multiplies lifetime of processing units to standard lifetimes.
For application in food branch or for special applications, coatings in thin film process are used. Here, all parts of the processing unit with contact to the plastic material are coated as written above. This coating is thinner, but harder and has got a low adhesion factor at the surface.